Potentiation of the immobility response elicited by bandaging and clamping in mesencephalic rats

In earlier work, we showed that adult rats exhibit immobility response (IR) if a clamp is fastened to the skin of the nape of the neck, but not at other areas of the body, and not by bandaging. The present study characterizes IR in adult rats with complete mesencephalic transections. In the mesencephalic rats, the duration of the IR not only increased, but the stimuli capable of eliciting it were more diverse. All head and body areas clamped or bandaged were capable of inducing a profound IR. In contrast, the IR in intact rats was of shorter duration, and was only induced by clamping the neck, or by bandaging the upper or the lower torso. Furthermore, unlike the mesencephalic rats the ability of the bandaging to induce IR is reduced after the first trial and finally disappears. Only clamping the neck was able to persistently induce IR in intact rats. These data support the hypothesis that the IR control system is in the midbrain, hindbrain or spinal cord, and that systems above the mesencephalon modulate the IR. Such modulation appears to involve the ability to discriminate amongst tactile stimuli, and to integrate previous experience.